There’s reason to believe that Pfizer’s COVID-19 pill is not that effective in combating the viral disease that continues to wreak havoc worldwide.

A large study published this week found that the pill provided little or no benefit for younger adults, or those in the 40 to 64 age group.

For the Israeli study published in the New England Journal of Medicine on Wednesday, researchers analyzed data from 109,000 patients at a large health care organization. Nearly all of the participants had been vaccinated, had been previously infected, or both.

The researchers tracked the patients’ records of hospitalization and death rates in relation to their age. According to the team, around 4,000 participants had taken Paxlovid, an antiviral therapy consisting of two medications co-packaged for COVID-19 treatment.

In the study, the drug is referred to by its name Nirmatrelvir and not by its brand name Paxlovid. Developed by Pfizer, the drug has become the go-to at-home treatment for COVID-19 infection following the U.S. government’s recommendation, as per USA Today.

However, the analysis of patient records prompted the researchers to report that the drug did not yield measurable benefits in younger adults.

On the other hand, the team observed reduced hospitalizations among people 65 and above who took Paxlovid. Their risk for hospitalization significantly dropped by 75% when taking the drug shortly after infection.

The study findings showed that Paxlovid was able to do what it’s supposed to by reducing serious illness from COVID-19 in people with an elevated risk of suffering a severe infection. Old age is one of the risk factors for severe COVID, according to TIME.

“Paxlovid will remain important for people at the highest risk of severe COVID-19, such as seniors and those with compromised immune systems,” Dr. David Boulware, a University of Minnesota researcher not involved in the large-scale Israeli study, told USA Today.

Nevertheless, the findings somehow question the drug’s practicality for people below 65, considering that it comes with potential side effects, including muscle aches, high blood pressure and diarrhea.

A spokesperson for Pfizer declined to comment on the study findings when reached by several media outlets.